sedimentary

Dark flint or chert fragment

Microcrystalline quartz (SiO₂), likely chert/flint

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, opaque dark gray to brown, with dull-to-waxy luster and conchoidal fracture; no visible crystal grains or cleavage. The sharp pointed edge and smooth fracture surfaces fit worked or naturally fractured chert.

Identified August 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or precipitates within limestone and other sediments, commonly during the Paleozoic–Mesozoic; exact age cannot be determined from the image. Its shape may reflect natural breakage or prehistoric human working.

Uses & applications

Used historically for cutting tools, arrowheads, fire-starting, and construction aggregate; attractive pieces are collected, but this specimen has little commercial value without confirmed archaeological context.

Geological facts

Chert is chemically similar to quartz but cryptocrystalline, composed of microscopic interlocking quartz crystals and sometimes chalcedony. Dark coloration commonly comes from organic matter, iron, or manganese impurities.

Field identification & locations

Identify by testing for glass-scratching hardness, conchoidal fracture, and lack of fizz in dilute hydrochloric acid; it commonly occurs as nodules or layers in limestone. Avoid claiming it is an artifact without edge flaking or archaeological documentation.